1. Field of the Invention
The present invention relates to a color image reader using a one-dimensional line image sensor exhibiting a photoelectric conversion nature. More particularly, the present invention relates to a color image reader which optically and electronically reads an image from an object by cyclically illuminating the object with three-primary colors of light and by continuously moving either the object or the line image sensor, thereby scanning the object with the line image sensor during the cyclical illumination of the object with the three-primary colors of light.
2. Description of the Related Art
In a conventional color image reader using a one-dimensional line image sensor exhibiting a photoelectric conversion nature, such as a CCD (charge-coupled device) line image sensor, an object is intermittently moved with respect to the line image sensor, thereby scanning the object, step by step, with the line image sensor, while the object is cyclically illuminated with the three-primary colors of light, for example, red-light rays, green-light rays and blue-light rays.
In particular, at each of the scanning steps, the object is successively illuminated with the three-primary colors of light in the order of, for example, the red-light rays, the green-light rays and the blue-light rays, and the line image sensor then produces, in succession, a single-line of red image-pixel signals derived from the red-light illumination, a single-line of green image-pixel signals derived from the green-light illumination, and a single-line of blue image-pixel signals derived from the blue-light illumination. Namely, at each of the scanning steps, three single-lines of red, green and blue image-pixel signals are obtained with respect to a single scanning-line of the object. Thus, a color image of the object can be reproduced, on the basis of the three-primary color image-pixel signals obtained with respect to the scanning-lines of the object.
Nevertheless, in the conventional color image reader, a protracted period of time is required to read a color image from the object, because of the relative intermittent movement between the object and the line image sensor.
To decrease the period of time for reading a color image from the object, it has been proposed that the object is continuously moved, with respect to the line image sensor, during the cyclical illumination of the object with the three-primary color light rays, in such a manner that a single-line of red image-pixel signals derived from the red-light illumination, a single-line of green image-pixel signals derived from the green-light illumination, and a single-line of blue image-pixel signals derived from the blue-light illumination are cyclically read in succession from the line image sensor.
In this case, a color image of the object is reproduced, for example, with respect to the green scanning-lines of the object, from which the respective single-lines of green image-pixel signals are obtained. No actual single-line of red image-pixel signals and no actual single-line of blue image-pixel signals are obtained at each of the green scanning-lines of the object, because of the continuous movement of the object with respect to the line sensor.
Therefore, the single-lines of red image-pixel signals and the single-lines of blue image-pixel signals, actually obtained from the red scanning-lines and the blue scanning-lines, respectively, of the object, are used to estimate, by interpolation, single-lines of red image-pixel signals and single-lines of blue image-pixel signals which occur at the green scanning-lines, but which are not actually obtained due to the green scanning-lines only being illuminated by the green light rays. Then, by combining the green image-pixel signals, the interpolated red image-pixel signals and the interpolated blue image pixel signals, at each green scanning-line position, a color image can be reproduced.
However, the conventional interpolation processing requires improvement, because the interpolated single-lines of red image-pixel signals and the interpolated single-lines of blue image-pixel signals cannot be confidently and reasonably estimated on the basis of the actual single-lines of red image-pixel signals and the actual single-lines of blue image-pixel signals, obtained from the red scanning-lines and the blue scanning-lines, respectively, adjacent to the green scanning-lines of the object, for the reasons as discussed hereinafter in detail.